LeetCode: Flatten a Multilevel Doubly Linked List Solution

Approach

Iterative way

If a node has a child:

• point node's
  next
  to child, child's
  prev
  to node
• iterate child to its tail, then point tail's next to original node's next, original node's next's prev to tail

But I think variables naming for better readability in this task is important also, for our future self

Implementation

1var flatten = function (head) {
2  for (let node = head; node; node = node.next) {
3    if (!node.child) continue
4
5    let child = node.child
6    let next = node.next
7
8    node.next = child
9    child.prev = node
10    node.child = null
11
12    while (child.next) child = child.next
13    child.next = next
14    if (next) next.prev = child
15  }
16  return head
17}